U.S. Pat. No. 3,518,019 discloses a synthetic resin nib of this kind. FIGS. 1 and 2 of the accompanying drawings illustrate the prior art. As appears, the nib comprises a tube 1 having a substantially conical writing tip 2 and radial slots 3 extending through the length of the tube 1. The cross section of each of the slots 3 is of wedge-like shape and tapers toward the central axis 4 so that the slots 3 gather at the axis 4. In the nib, when the writing tip 2 is directed upwardly, the ink A rises higher adjacent the central axis 4 by the stronger capillary action, as shown by the dot-dash lines in FIG. 1, since the cross sectional inner ends of the slots 3 become narrower, thus causing the ink A to be thicker about the central portion of the writing tip 2. This structure has an advantage in that it assures immediate use of a writing instrument. However, upon beginning to write with the nib by directing it downwardly, just the center of the writing tip 2 should be contacted to a paper. Therefore, it takes some time after holding the nib downwardly until the ink A comes down along the slots 3 to fill them entirely at the writing tip 2 so as to make it possible to write at any angle of the writing tip, i.e., with the entire surface about the writing tip.
A primary object of the present invention is to obviate the above defect, and to provide a nib enabling the immediate use at any angle even after it was directed upwardly for a long while.